1. Field of the Invention
The present invention relates to the manufacture of surface-fluorinated metal oxide particulates. More specifically, the present invention relates to surface-fluorinated metal oxide particulates whose surface affinity being controlled from `hydrophilic` to `hydrophobic` and which has improved stability, water repellent and dispersibility, a process for manufacturing the same and use of the same.
2. Description of the Related Art
Metal oxide particulates are used for a wide variety of applications and useful as raw materials of paints, matting agents for synthetic fibers, printing ink, cosmetics, opal glass, etc. and as coloring agents for rubbers and resins, pigments; and the like.
The surface of a metal oxide particulate is usually covered with a hydroxyl group and exhibits hydrophilicity. Accordingly, when the metal oxide particulates are blend in a resin, a paint or a cosmetic, a large number of surface treatments such as treatment with a higher fatty acid, treatment with an organic silicon compound, silica-alumina treatment and treatment with various coupling agents, are being attempted and practiced so as to improve dispersibility, for example, of titanium oxide. Also, there has been attempted surface treatment of aluminum oxide or silicon oxide with a silylating agent or the like.
These methods all intend to control the hydrophobicity or hydrophilicity or control the surface activity by the substitution-elimination of hydroxyl groups on the surface of a metal oxide particulate.
However, when this metal oxide particulate is added to fluororesin or the like, higher hydrophobicity and higher lipophobicity are demanded and accordingly, it is necessary to form a surface covered with fluorine having a surface energy lower than water or oil.
As the technique for solving this problem, for example, JP-A-59-184263 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a method of adding sodium fluoride to a suspension slurry of titanium oxide and stirring the mixture. However, according to this method, in the case when titanium oxide is an ultrafine particulate, coagulation in the drying process is intensified and good dispersibility cannot be obtained even if the matters coagulated are crushed. Further, according to this method, the fluorine atom is not bonded directly to the titanium atom and it cannot be said that the titanium oxide surface is fluorinated or modified with fluorine.
JP-A-61-215216 discloses a method of using an organic fluorine compound as a hydrophobicity-imparting substance in the production of hydrophobic spherical titanium oxide particulates. However, also in this case, the titanium oxide surface is substantially not modified with fluorine.
JP-A-3-40919 discloses a method of bringing freon gas into contact with titanium oxide ultrafine particulates and modifying their surface with fluorine at a high temperature of from 200 to 400.degree. C. However, use of the reaction temperature as high as 200.degree. C. or more results in the thermal efficiency which is not always good.
With respect to aluminum oxide and silicon oxide, nothing has been known about the fluorination of the surface of the particulates thereof.